System for communicating with network having first operating system in charge of upper communication layers and second operating system in charge of lower communication layers

ABSTRACT

A communication system for communicating with a network which includes a computer associated by means of a bus with a communication processor which is itself linked to a specific link of the network, the computer including a first operating system, and the processor including a second operating system, which handles the transmission of data from the bus to the network and vice versa. The communication system includes a telecommunication server associated with the first operating system, and a communication code which belongs to at least one open systems interconnection model associated with the second operating system, wherein the server provides the first operating system with access means to the various layers of the code, this code implementing the specific protocols of each layer, in order to enable transmission to the host or to the network.

BACKGROUND OF THE INVENTION

The present invention relates to a system for communicating with anetwork. The invention is particularly applicable to a network of theFDDI type in which the transmission medium is constituted by fiberoptics, a network which is standardized by ANSI under the referencenumber X3T9-5, and by ISO, the International Standards Organization.

It is known that networks are constituted by a plurality of terminals orstations linked to one another by a transmission link (in the case of anFDDI-type network, the corresponding transmission medium is constitutedby fiber optics). A computer linked to a network is considered aterminal.

Numerous modern networks operate in accordance with the same referencemodel. The most widely known are the OSI or TCP-IP reference models.These models are similar with regard to the definition of theirarchitecture in the form of standardized layers. Thus, in the OSI model,there are seven different activity layers, the bottom layer (layer 1)corresponding to the physical transmission of signals, and the top layer(layer 7) corresponding to the functions carried out by the applicationprograms (more simply called applications) and the users of the networkin question.

The trend in the technological development of networks and theutilization of greater and greater numbers of terminals is leading tothe development of communication processors, which are most oftenassociated with a computer for the purpose of reducing the load on itscentral processor by carrying out part of the management of itscommunications with the other terminals in the network. In a givennetwork, computers of different types using different operating systemscan be made to communicate.

The association of a computer and a communication processor constituteswhat may be called a system for communicating with a network.

In this association, the role of the communication processor (which canalso be called a data transmission system) is to adapt the conditionsfor transmitting information through the bus of the computer to which itis connected to the conditions for transmitting through the network,which are totally different. A communication processor of this typeallows applications which are supported by several operating systems invarious computers to communicate with one another. In particular, itallows the various communication layers of the operating system of afirst computer to communicate with the various communication layers ofthe operating systems of other computers which are directly orindirectly connected to this same network. For example, a communicationprocessor of this type is known which has the simplified architectureshown in FIG. 1, and which is described, for example, either in theFrench patent application No. 9213653 filed Nov. 13, 1992 by theApplicant under the title "Tool for Simulating a Network Code," or inthe French patent application No. 9215521 with the title "System forTransmitting Data between a Computer Bus and a Network," filed Dec. 22,1992 by the instant Applicant.

A communication processor of this type, designated NCC, makes itpossible to assure the management of data transfers between a computerHOST, which is equipped with an internal bus PSB and whose operatingsystem is designated SE₁, and a network RE, which is an FDDI-typenetwork, for example. The bus PSB is, for example, a bus of theMULTIBUSII type (a trademark registered by the Intel Corporation)standardized according to IEEE (Institute of Electrical and ElectronicEngineers) standard 1296.

A processor NCC of this type includes the following three essentialparts:

the first part, called a GPU (English acronym for General Purpose Unit)is, for example, the model described in French patent application No.9108908 filed Jul. 15, 1991 by BULL S. A., under the title "UniversalDevice for Coupling a Computer Bus to a Controller of a Group ofPeripherals". This part is equipped with an operating system, forexample a system of the type described in French patent application No.9108907 filed the same day as the above, by the same applicant, underthe title "Operating System for a Universal Device for Coupling aComputer Bus to a Specific Link of a Network". The purpose of this partGPU is to assure the initialization of the coupler assembly NCC on onehand, and to assure a communication with the computer HOST through thebus PSB on the other hand, while complying with the utilizationstandards for this bus and conforming to the nature of the operatingsystem SE₁ of the computer HOST. Furthermore, the part GPU assures thephysical transfer of data between the bus PSB and the second part DEA,called an adaptor device, which is directly connected to the network RE.The function of this part DEA is described below.

the part DEA is, for example, a part of the type described either inFrench patent No. 2 650 412 with the title "Gateway Device forConnecting a Computer Bus to a Fiber Optic Ring Network" as far as thehardware is concerned, or in French patent application No. 92 11054 asfar as the software is concerned. This part DEA assures the physicaltransmission of data between the part GPU and the network RE, as well asthe physical connection to the network.

the third part, called PPA, is actually a communication coprocessorwhich is more particularly intended for the management of the varioustelecommunication layers of the OSI model, or the TCP-IP model. For theOSI model, as well as for the TCP-IP model, the part PPA assures themanagement of the communication layers C₄, C₃, C₂, that is, thetransport, network, and data link layers, respectively.

The communication layers C₂ through C₄ communicate with one another bymeans of primitive functions which allow two adjacent layers tocommunicate with one another. Thus the two layers C₂ and C₃ communicatewith one another by means of the set of functions ST2, while the layersC₃ and C₄ communicate by means of the set of functions ST3. Moreover, C₄communicates with the external environment, for example with externalapplications, by means of an interface SH.

In a preferred embodiment of the instant the invention, the sets offunctions ST2, ST3, SH are functions which are known in current practiceby the name STREAMS. These standard functions are defined by thefollowing documents, for example:

Unix System V Release 4--STREAMS Programmer's Guide, ATT Issue 1

Unix System V Release 3.2--STREAMS Programmer's Guide, ATT (ISBN0-13-944810-1), 1989.

In the examplary embodiment shown in FIG. 1, when the computer HOSTsends a message to the network RE, or even when a message comes from thenetwork RE, it passes through the layers C₂ through C₄ of PPA through aFIFO memory, either FF₁ or FF₂, in accordance with which this message istransmitted to DEA or to GPU, respectively. When seeking to establish aconnection request, or to send messages to all or some of the stationsconnected to the network, whether originating from or going to the hostcomputer HOST, this connection or these messages pass through SH.

The layers C₂ through C₄ and the various functions ST2, ST3 and SH, aswell as the operating system of the part PPA, constitute thecommunication layer code CC which is implemented by the communicationcoprocessor PPA.

The essential role of the communication coprocessor PPA is to relievethe host system of the management of the communication layers which itnormally carries out, while maintaining extremely high performance inthe communication processor NCC, as far as the data transmission rate toor from the network is concerned.

Furthermore, it may be noted that the part GPU includes a part HIA whichlinks it to the bus PSB. HIA, which can also be called a host adaptor,varies with the nature of the internal bus of the host adaptor. In thecase in which PSB is a MULTIBUSII bus, the part HIA is formed by acoprocessor of the VN82C₃ 89 type, manufactured by the IntelCorporation.

The association of the computer HOST equipped with its operating systemSE₁, which is for example a system of the GCOS7 type developed byApplicant, with the communication processor NCC constitutes thecommunication system SCI of which the present invention constitutes aparticularly advantageous embodiment, which makes it possible to obtainhigh performances relative to the data transfer rate.

SUMMARY OF THE INVENTION

It is a primary object of the present invention to provide a system forcommunicating with a network, which includes a computer connected bymeans of a bus to a communication processor which is itself linked tothe specific link of the network, the computer including a firstoperating system associated with a plurality of applications whichexchange data with the terminals connected to the network and a firstinput/output manager which organizes within the bus the transfer of datato a second input/output manager of the processor, which includes asecond operating system which organizes the operation of the processorin order to transmit the data from the bus to the network and viceversa, wherein the system includes:

a communication server associated with the first operating system,

a communication code, which belongs to at least one open systemsinterconnection model, associated with the second operating system, theserver providing the first operating system with means of access to thevarious communication layers of the code which implement the specificprotocols for each layer, in order to assure transmission to the host orto the network.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the present invention willbecome apparent in the following description given by way of anon-limiting example and in reference to the appended drawings, inwhich:

FIG. 1 shows, in a simplified form, the various essential elements whichconstitute a communication system.

FIG. 2 shows the essential elements constitute the software architectureof the communication system according to the instant invention,

FIG. 3 shows the elements which define the communication code present inthe communication coprocessor, which belongs to the system of theinstant invention,

FIG. 4 shows the elements which define the telecommunication serverwhich belongs to the system of the instant invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now, more particularly to FIG. 2, which shows the softwarearchitecture of the computer HOST and the communication processor NCC.

The elements of the software architecture of HOST are the following:

a plurality of applications A_(i) and B_(i), which for example conformto the standards of the OSI reference model for A_(i) and the standardsof the TCP-IP reference model for B_(i). In order to be fullyimplemented, these applications need a certain number of pieces ofinformation and data which are not necessarily found in the memories orin the peripherals associated with the computer HOST. These pieces ofinformation and data can be found in terminals connected to the networkRE or even in more remote networks interconnected with this same networkRE. Therefore these applications need to establish a dialogue with otherapplications implemented by terminals connected to RE.

the sessions S₁ and S₂ respectively correspond to the applications A_(i)and B_(i), which establish precisely the conditions for a dialogue withthe corresponding applications of the other terminals in RE. The set ofsessions S₁ conforms to the standards of the OSI model, while the set ofsessions S₂ conforms to the standards of the TCP-IP model.

the two interfaces IS₁, IS₂, respectively provide transport services tothe sessions S₁ and S₂ for the OSI and TCP-IP models.

the module TPAM, which supports the transport protocol between thecomputer HOST and the communication processor NCC, and more particularlythe transport protocol between HOST and the part PPA of NCC. TPAM is theEnglish acronym for Transport Protocol Access Module.

the input/output manager GES₁, which is associated with the interfaceIP₁.

The set of elements IS₁ -IS₂, TPAM, GES₁ is considered to form acommunication server designated NCCD (the letter D stands for Driver inEnglish, a term which corresponds to module). Given that it is possibleto associate several communication processors, which are identical toNCC, with the computer HOST, it is evident that in this case, thesoftware architecture of HOST includes several communication serversidentical to NCCD, each of which is associated with a predeterminedcommunication processor. In order to simplify the explanation, it willbe assumed here and in the remainder of the description below that HOSTis associated with only one communications processor NCC, and includesonly the one corresponding communication server, namely NCCD.

The various essential elements which constitute the softwarearchitecture of the communication processor NCC are the following:

the physical interface IP₂ which corresponds to the physical interfaceIP₁,

the input/output manager GES₂, which corresponds to the input/outputmanager GES₁.

The two physical interfaces IP₁ and IP₂ are MULTIBUSII interfacesdefined by the above-mentioned IEEE1296 standard. They can therefore beembodied in the same way as the element HIA shown in FIG. 1 and can eachbe constituted by a coprocessor MPC.

The set of the two layers constituted by the MULTIBUSII physicalinterface and the input/output manager, whether it consists of GES₁ andIP₁, or GES₂ and IP₂, is known by the name of the protocol PLANETintroduced by the Applicant company and described in French patent No. 2633 414, which has the title "Centrally Interconnected InformationSystem".

The operating system GPOS which is disposed in the part GPU of NCC isdescribed in the above-mentioned patent application No. 91 08907.

the interface HI (English acronym for Host Interface), disposed in thepart PPA, called a host interface, which assures the dialogue betweenthe various layers C₄ of the communication code CC and one of theinterfaces IS₁ or IS₂ of HOST. The interface HI therefore assures thetransport service between the communication code CC and the sessions S₁and S₂ of the host HOST. The interface HI also assures the handling ofthe data paths between the host HOST and PPA. The interface HI is asoftware component which is stored in PPA. This interface opens andcloses the connections on behalf of HOST as well as on behalf of C₄,executes the data transfers and controls the data flow between the hostHOST and the communication code CC, whether it involves the part of thecommunication code which relates to the OSI model or that which relatesto the TCP-IP model. The interface SH mentioned above is actuallysituated between HI and C₄.

The interface HI also allows the data flow to use the transport entitiesof the code CC (Layer C₄), by adapting the transport protocols whichrelate to these layers to the transport protocol TPA used between thehost HOST and NCC.

the communication code CC composed of the layers C₂ through C₄. Thus asstated above, this code relates to the OSI reference model as well as tothe TCP-IP model. It has also been stated that it provides thecommunication stacks C₂ through C₄ for one of these models, these stacksbeing designed most often by the English word STACK. The code CCtherefore includes an OSI stack and a TCP-IP stack. It is appropriate tonote that the layer C₂, called LLC, also called the data link layer, iscommon to these two stacks.

a communication interface HIN between GPOS and CC.

the interface ID and the input/output manager GES₃. They form thesoftware of the adaptor device DEA, which is described in theabove-mentioned French patent application No. 92 11054, and which makesit possible to connect NCC to the network RE. It is appropriate to addto these last elements the physical interface IP₃ for connecting DEAwith the network RE, which is also described in this same application.

The mainlines of operation of the architecture, shown in FIG. 2, are thefollowing:

Suppose that any application A_(i) belonging to the computer HOST wishesto exchange information with any application, called a remoteapplication, situated in any terminal linked to the network RE. Thisapplication passes through a corresponding session belonging to the setS₁, a session which will carry out the function which is usuallydevolved to it by the OSI reference model (naturally, the reasoning usedhere would be the same for an application B_(i) and a session S₂), thatis, it will negotiate the establishment and the termination of thedialogue A_(i) and the remote application with the corresponding sessionof the receiving terminal connected to the network RE. The session thenuses the interface IS₁ to dialogue with the interface HI in order toestablish the corresponding transport service. In the present case, IS₁is therefore the requester of the transport service, whereas theinterface HI is the provider of the transport service which will be usedbetween the system SCI and the remote terminal with which theapplication A_(i) is carrying on a dialogue. The module TPAM then takesover from the interface IS₁ in order to dialogue with the system GPOS toestablish the transport connection between the computer HOST and thecommunication processor NCC. The transport protocol used between theselast two elements is called TPA (Transport Protocol Access). Thisprotocol is a protocol derived from the protocol called TPI (TransportProvider Interface) defined by the company ATT. This protocol allows acontrolled exchange of data between the host and the interface HI. It isprincipally based on the notion of a communication port (CommunicationPlug). In fact, a port is an element which identifies a connectionbetween the module TPAM and the interface HI. This identificationelement has a predetermined value.

The protocol TPA defines a message interface to or from the transportprovider (the layer C₄ of the communication code CC): this indicatesthat the user (here the application A_(i)) is communicating with thetransport provider or that the latter is communicating with the user bymeans of transport service primitives which transport messages. Thesemessages are transmitted to or from the computer HOST (that is, to orfrom TPAM) by means of the ports. These ports therefore make it possibleto control the exchange of messages between TPAM and GPOS. During itsutilization, each port is dedicated to a predetermined transportconnection. Thus, different ports which are precisely predeterminedcorrespond to the transport provider of the OSI model, or to thetransport provider of the TCP model, or even to the transport providerof the DIWS model (this model, which is also used by the communicationsystem SCI according to the invention, corresponds to the model calledISO/DSA defined by the Applicant). Furthermore, each transportconnection (also called a transport session), whether of the OSI, DIWS,or TCP-IP model, is managed by a single connection of the TPA type.

As soon as the exchanges which allow a transport connection to beestablished between TPA and GPOS are terminated, the input/outputmanager GES₁ and its interface IP₁, as well as the correspondingelements GES₂ and IP₂ take over, in order to transport the data via thebus PSB to the communication processor NCC, according to the protocol"PLANET", in a manner which is summarized in the above-mentioned patentapplication No. 91 08907. The data are then stored in the memory of theelement GPU (this memory is a double access-type memory, and isdescribed more completely in the above-mentioned patent application No.91 08908).

It is appropriate to note that FIG. 2 represents direct links betweenIS₁ and HI, TPAM and GPOS, and between GES₁ and GES₂. This indicatesthat the element IS₁ communicates directly with HI, that TPAMcommunicates directly with GPOS, and that GES₁ communicates directlywith GES₂. It is quite evident, however, that the pieces of informationexchanged between each of these elements are conveyed by the otherelements which belong to the lower layers. Thus the data exchangedbetween IS₁ and HI are physically conveyed by TPAM and GPOS, just as thepieces of information exchanged between TPAM and GPOS are physicallyconveyed by GES₁ and GES₂, and so on.

As soon as the data frames which contain the information relative to thesession and to the transport protocol TPA reach the element GPU, thiselement transmits them to the interface HI which itself transmits themto the various layers C₄ of the communication code CC. Thiscommunication code CC frees the useful data from the informationelements which relate to the transport protocol TPA, and provides themto each of the layers C₄ of the corresponding protocols. This is equallytrue for the OSI, DIWS, and TCP-IP models. It is appropriate to notethat the layer C₂ is common to these various models. As soon as theelement PPA which implements the communication code CC has terminatedits operation, the data frames thus constituted are again transmitted,under the control of GPOS, to the double access memory of GPU throughHIN and FF₂. Then, under the control of GPOS, these data are transmittedto the interface ID, to the input/output manager GES₃ and to thecorresponding physical interface IP₃ of the adaptor device DEA, in amanner which is indicated in the above-mentioned patent application No.9211054. The data are then transmitted through the network RE and arriveat their final destination.

Conversely, the data frames which originate from RE pass through IP₃,GES₃ and ID before being stored in the double access memory and thentransferred, under the control of GPOS, through the FIFO FF₂ and HIN tothe layer C₂ (LLC₂) of CC. PPA then successively implements the layersC₂, C₃, and then C₄ which provides the useful data previously freed fromthe information elements which relate to TPA, that is, freed from theprotocol elements of the layers C₂, C₃, C₄ which are necessary for theflow of the data frames through the network RE. C₄ then transmits thedata frames thus obtained to HI which sends the data to GPU which, underthe control of GPOS, transmits the data through GES₁ and GES₂ to TPAM,which feeds the data back to IS₁ -IS₂, S₁ -S₂, then A_(i) -B_(i).

FIG. 4, which shows in more detail the elements which define the moduleNCCD, and, more particularly, the elements which define IS₁, TPAM andGES₁ and how they are linked to one another inside the module NCCD, willnow be discussed below.

FIG. 4 represents the set of applications A₁, A₂, . . . , A_(i), A_(n),as well as the applications B₁ through B_(n).

The applications communicate with the set of sessions S₁, which areVCAM-type sessions (in conformity with the OSI, ISO/DSA model). This setof sessions S₁ communicates with the interface IS₁, which is of the TSI(Transport Session Interface) type, and which is the interface betweenthe VCAM-type sessions and the module TPAM. TSI also assures theinterface between the sessions S₂ and the module TPAM for the OSIreference models. This interface is described in the documents2297M/1.0, 2298M/1.0 and 2299M/1.0 of the Applicant company.

The two sets constituted by GX-RPC and S₂ constitute a set of sessionswhich belongs to the GCOS7 operating system adapted to the UNIXenvironment, and to the TCP-IP reference model. The correspondinginterface IS₂ is an interface of the GXTIA type (meaning GXTI Access),an interface which belongs to the TCP-IP reference model. GXTI and GXTIAare described in the Applicant's document "Marketing 47A2 64UC Rev. 0"and GX-RPC is described in the documents which relate to GCOS7.

The module TPAM, in addition to supporting the protocol TPA and managingthe TPA-type branches as mentioned above, controls the input/outputmanager GES₁.

Furthermore, the module NCCD includes an administrative agent SNMP-DSACwhich communicates with the module TPAM through the interface IS₂. Thisagent is known and it is charged with administrating the various layersof the OSI and ISO/DSA reference models (DSAC), and the TCP-IP and FDDIreference models (the agent SNMP, through the SNMP MIB₂ standard, anFDDI extension).

FIG. 3, which shows the various software modules which are implementedby the part PPA of the communication controller NCC, will now beexplained.

This software module implemented by PPA is here designated LOGC andincludes:

the operating system SE₂ which is, for example, the CNS-A₁ type ofsystem developed and marketed by the Applicant company.

the interface HI described above.

the three communication modules MOSI, MDIWS, MTCP which relate to thepart of the communication code CC which implements the layers C₄ and C₃of the OSI, ISO/DSA, and TCP-IP reference models.

the communication layer LLC₁ which corresponds to the layer C₂ of theOSI, ISO-DSA and TCP-IP reference models. As stated above, the layerLLC₁ is common to the three above-mentioned reference models.

the communication interface HIN between the part PPA and the part GPU.This interface HIN assures the transfer of data between GPU and PPA, forthe reception of data frames originating from the network as well as forthe emission of data frames into this network. The way in which theinterface HIN carries out the data transfer between GPU and PPA, underthe control of the operating system GPOS of GPU, is analogous to thatdescribed, for example, in either of the patent applications 90 10179and 9012826, respectively filed on Aug. 9, 1990 and Oct. 17, 1990 byApplicant under the titles "Controller of Communication between aComputer and a Plurality of RNIS-type Terminals" and "Controller ofCommunication between a Computer and a Plurality of Terminals whichBelong to a CSMA/CD-type Network". Both of these applications actuallydescribe the manner in which the data transfer is executed through acommunication controller between a base controlled by a firstmicroprocessor and a peripheral controlled by a second microprocessor,these first and second microprocessors playing the same role as themicroprocessors which respectively contain the parts GPU and PPA (seethe above-mentioned patent applications 91 08908 and 92 15521).

the configuration module DAEMON which constructs the stack of thevarious layers belonging to each of the various modules MOSI, MDIWS,MTCP and LLC₁. It is necessary to construct this stack by creating linksbetween the various modules by means of various STREAMS-type functions,namely SH between HI and the three modules MOSI, MDIWS, MTCP, andfunctions ST2 between these modules and the module LLC₁. Moreover, it isalso necessary to create links between the layers C₄ and C₃ of thesevarious modules, by means of the primitive functions ST3. In effect, atthe initialization of the communication processor NCC and consequentlyat the initialization of the part PPA, the modules are isolated from oneanother. This is due to the design philosophy of STREAMS-type functions:By this philosophy, a module does not know with what it is supposed todialogue, but it does know that it must dialogue with other modules. Itis therefore necessary to create these links during initialization.

an administration module ADM which enables the handling of the pieces ofinformation contained in the layers C₄ through C₂, making it possible toconfigure them, initialize them, etc. This module therefore communicateswith HI through SH and with MOSI, MDIWS, and MTCP by means of thestreams functions.

Furthermore, the links between HI and LLC₁ on one hand, and theinterface HIN on the other hand, are also established by means ofSTREAMS-type functions.

While the preferred forms and embodiments of the invention have beenillustrated and described, it will be apparent to those of ordinaryskill in the art that various changes and modifications may be madewithout deviating from the inventive concepts and spirit of theinvention as set forth above, and it is intended by the appended claimsto define all such concepts which come within the full scope and truespirit of the invention.

We claim:
 1. A communication system for communicating (SCI) with a network having a plurality of terminals connected thereto, said system (RE) including a computer (HOST) associated by a bus (PSB) with a communication processor (NCC), said communication processor being linked to a specific link of the network, the computer including a first operating system (SE₁) in charge of upper communication layers and associated with a plurality of applications (A_(i), B_(i)) which exchange data with the terminals and a first input/output manager (GES₁) which organizes within the bus a transfer of the data to a second input/output manager (GES₂) of the processor (NCC), said processor (NCC) including a second operating system (GPOS) in charge of lower communication layers and which organizes the operation of the processor (NCC) in order to transmit the data from the bus to the network and vice versa, said system comprising:a telecommunication server (NCCD) associated with the first operating system (SE₃) operable to provide transport services to session layers managed by said computer and to handle transport layers between said computer and said communication processor, and a communication code (CC) including lower communication layers from the transport layer, wherein the telecommunication server includes means for enabling the first operating system to access various layers of the communication code (CC), the communication code implementing a component and specific protocols of the component for each of the layers of the communication code, in order to assure transmission to the host or to the network.
 2. The communication system according to claim 1, wherein the telecommunication server (NCCD) includes:at least one interface (IS₁, IS₂) which provides transport service to at least one session (S₁, S₂) which belongs to the open systems interconnection model (OSI, TCP-IP), said session corresponding to at least one of said applications (A_(i), B_(i)); a module (TPAM) which supports a transport protocol between the computer and the processor; and an input/output manager (GES₁) associated with a specific physical interface (IP₁) of the bus (PSB), said input/output manager being controlled by said module (TPAM).
 3. The communication system according to claim 2, wherein the communication processor (NCC) includes:a physical interface (IP₂) with the bus which corresponds to the physical interface (IP₁) of the telecommunication server (NCCD); an input/output manager (GES₂) which corresponds to the input/output manager of the telecommunication server; wherein a set of two layers (GES₁ -IP₁, GES₂ -IP₂) defined by the physical interface and the input/output manager of the telecommunication server and the communication processor, respectively, constitute a protocol known as PLANET; the communication code (CC) including the transport, network, and data link communication layers (C₄. C₃, C₂); an interface (HI) which enables communication between the various layers of the communication code and the interface (IS₁) of the session which belongs to the telecommunication server (HIN); and means for connecting the processor (NCC) to the network (RE).
 4. The communication system according to claim 3, wherein the communication code (CC) is supported by a third operating system (SE₂) which is of the CNS-A₁ type, and includes three communication modules (MOSI, MDIWS, MTCP) which respectively relate to a part of the communication code which implements the layers C₄ and C₃ of the OSI, ISO/DSA, and TCP-IP reference models, the communication layer C₂ being common to the reference models.
 5. The communication system according to claim 4, wherein the communication processor further includes a configuration module (DAEMON) which constructs a stack of the various layers belonging to each of the three communication modules and further wherein respective links between the communication modules, the communication interfaces (HIN) and the interface (HI), as well as between various layers which comprise each of the modules being provided by STREAMS-type functions. 